As color toners for color copiers and color printers, at present, mainly employed are toners produced in a pulverizing method. In recent years, however, requirements for an enhanced image quality have been continuously increased and particles of smaller particle size and narrower particle distribution have been able to be produced at a lower cost. Therefore, manufacturing methods for the toners employing an emulsion polymerization method, a suspension polymerization method and a dispersion polymerization method, and the like, have been strongly encouraged [for example, an emulsion polymerization method described in Japanese Patent Publication Open to Public Inspection (hereinafter referred to as JP-A) Nos. 63-186253, 6-329947, a suspension polymerization method described in JP-A No. 9-15904, and a dispersion polymerization method described in JP-A No. 8-320594].
As properties required for the color of such toners, not only color reproduction and image transmittance for overhead projectors (hereinafter referred to as OHP) but also light fastness is enumerated in order to consistently maintain these properties. The above-mentioned OHP image transmission rate refers to the OHP image transparency rate, and the degree of the variation in hue between the color of light transmitted through the OHP image and the color of light obtained by the reflection of said transmitted light on paper.
When a toner comprising a pigment as the colorant is employed, good light fastness is obtained. However, on account of insolubility of the pigment, a dispersed particle having a diameter of tens of nm to hundreds of nm is formed and problems are caused such as a decrease in the transparency and the hue variation in the color of transmitted light. When a toner is employed which comprises a pigment, for example, such as quinacridone red, which is one of the quinacridone type pigments, described in JP-A No. 63-186253, a disazo pigment, C.I. PIGMENT YELLOW 12, 13, 14, 16, and 17 described in JP-A Nos. 2-210363, 62-157051, 62-255956, C.I. PIGMENT YELLOW 185 described in JP-A No. 6-118715, the pigment is insoluble and tends to coagulate, forming dispersed particle having a diameter of tens of nm to hundreds of nm, through the secondary particle and further, the tertiary particle. As a result, problems such as a decrease in saturation and transparency of the OHP image are caused.
As countermeasures against such problems, the pigment is previously treated with a flushing method, a master batch method, etc., and the resulting treated pigment is then employed. When employing the countermeasures, the increase in cost is not avoided because of the increase in the number of manufacturing processes.
On the other hand, when a toner comprising a dye as the colorant is employed, the transparency of the OHP image is excellent because the dye is soluble and is sufficiently dispersed. However, there occurs a problem such that the light fastness is inferior to that of pigments. There are known dyes such as tannic acid salt of ORANGE II described in JP-A No. 63-186253, PTA salt of VICTORIA BLUE described in JP-A No. 63-186253, C.I. SOLVENT YELLOW 162 described in JP-A No. 3-276161, C.I. DIRECT YELLOW 160 described in JP-A No. 2-20747 and C.I. SOLVENT YELLOW described in 2-207273. These dyes produce OHP images having high transparency and no hue variation. However, as compared to the pigment type, the light fastness is inferior and consistent properties can not be obtained over a long period of time.